Electronic mail (“e-mail”) messages may be encoded using one of a number of known protocols. Some of these protocols, such as Secure Multiple Internet Mail Extensions (S/MIME) for example, rely on public and private encryption keys to provide confidentiality and integrity, and on a Public Key Infrastructure (PKI) to communicate information that provides authentication and authorization. Data encrypted using a private key of a private key/public key pair can only be decrypted using the corresponding public key of the pair, and vice-versa. The authenticity of public keys used in the encoding of messages is validated using certificates. In particular, if a user of a computing device wishes to encrypt a message before the message is sent to a particular individual, the user will require a certificate for that individual. That certificate will typically comprise the public key of the individual, as well as other identification-related information. As a further example, if a user of a computing device wishes to encrypt a message to be sent to multiple individuals, the user will require a certificate for each of those individuals.
Consider the situation where the user wishes to send an encrypted message to all individuals associated with a distribution list. Where possible, it is preferable that the message be encrypted such that each individual associated with the distribution list will be able to read the message when it is received. However, this may not always be readily performed. For example, the sender may not possess or may be otherwise unable to retrieve the certificate of each individual associated with the distribution list. In other cases, certain individuals associated with the distribution list may not be equipped to send and receive encoded messages, and therefore a certificate may not exist for those individuals.
In one known system, if an attempt is made to send an encrypted message to all the addresses of a distribution list and it is determined that not all of the individuals associated with the distribution list will be able to read the message, the sender of the message is given three options: (1) to send the message unencrypted to all of the addresses of the distribution list; (2) to send the message encrypted to all of the addresses of the distribution list; or (3) to not send the message. This known system, however, is not adapted to send a message only to the recipients who will be able to read the encrypted message.